A very hard word problem

There is a cycle shaped area with grass.The ray of the cycle is 10 m.In any point of the cycle there is a cow tighen with rope. How long should the rope be that the cow could eat half the grass of the cycle ?

I really hope u understand and help me solve this, because i read it in another langage and had to put it in english

There is a cycle shaped area with grass.The ray of the cycle is 10 m.In any point of the cycle there is a cow tighen with rope. How long should the rope be that the cow could eat half the grass of the cycle ?

I really hope u understand and help me solve this, because i read it in another langage and had to put it in english